Abstract

The baboon response to intravenous infusion of Shiga toxin 1 (Stx-1) varied from acute renal failure, proteinuria, hyperkalemia, and melena with minimal perturbation of host inflammatory and hemostatic systems (high-dose group, 2.0 microg/kg; n = 5) to renal failure with hematuria, proteinuria, thrombocytopenia, schistocytosis, anemia, and melena (low-dose group, 0.05 to 0.2 microg/kg; n = 8). Both groups exhibited renal shutdown and died in 57 hours or less. Both groups produced urine that was positive for tumor necrosis factor and interleukin-6 although neither of these cytokines was detectable (</=5 ng/ml) in the general circulation. Light and electron microscopy showed organelle disintegration and necrosis of the renal proximal tubular epithelium and of the intestinal mucosal epithelium at the tips of the microvilli, both of which were previously shown to bear Gb3 receptors. The renal distal tubular epithelium was spared. The renal proximal tubular epithelial changes were accompanied by swelling of visceral epithelial cells (podocytes) and by swelling and detachment of endothelial cells of the glomerular capillaries. In addition, all of the animals receiving low-dose Stx-1 showed microvascular fibrin deposition and thrombosis in renal glomerular and peritubular capillaries in association with a fall in hematocrit and platelet count and a rise in schistocyte count. The gastrointestinal villous tip lesions were accompanied by varying degrees of mucosal and submucosal congestion, hemorrhage, or necrosis. Electron microscopic images of cerebral cortex and cerebellum showed diffuse unraveling of myelin sheaths with occasional disintegration of neuronal cell bodies. In contrast to the gastrointestinal mucosal and renal proximal tubular epithelium, the Gb3 receptor glycolipid of the renal glomerular and neuronal tissues as determined using toxin overlay thin-layer chromatography plates was below the limit of detection (<13 pM/g wet tissue). We conclude that, depending on the status of the host and amount of toxin infused, Stx-1 can produce a variety of responses ranging from damage to cells carrying the Gb3 receptor (renal proximal tubular epithelial cells and gastrointestinal mucosa) to damage to renal glomerular tissues with microvascular thrombosis as a result of the host's inflammatory response localized to the kidney. We conclude that this thrombotic coagulopathy arises from local changes in the kidney because the appearance of host inflammatory mediators was limited to the urine. This suggests that the initial host response is localized in the kidney, and that the systemic thrombocytopenia, anemia, and schistocytosis may arise secondarily.

In comparison with glomeruli of control animals (A), those from animals receiving 2 μg/kg Shiga-like toxin (Stx-1) were congested but did not show a thrombotic microangiopathy (B), whereas those from animals receiving 0.05 to 0.2 μg/kg Stx-1 showed almost universal obliteration of capillary lumina, frequent fragmentation of red blood cells, and occasional fibrin thrombi (arrows in C). In comparison with tubules of control animals (D), those from animals receiving 2 μg/kg Shiga-like toxin (Stx-1) showed extensive epithelial necrosis (E), but this lesion was much less prominent in animals receiving 0.05 to 0.2 μg/kg Stx-1 (F). H&E; magnification, ×100.

Light micrographs of 1-μm plastic sections of renal glomeruli. A: Glomerulus from an animal challenged with high concentration of toxin. Note the congestion of red blood cells in some of the capillary loops (arrow) and the tuft expansion, which has reduced the urinary space within Bowman’s capsule. B: Glomerulus from an animal challenged with low concentration of toxin. Note the fibrin thrombi in several of the capillary loops (arrows) but the absence of tuft expansion and retention of ample urinary space in the capsule. Also note the osmophilic inclusions (i) in the visceral epithelial cells. Paragon stain; bar, 20 μm.

Electron micrograph of glomerular capillary loops from animals exposed to high (a) or low (b and c) toxin dose. a: Illustrates a minimal change seen in animals exposed to high concentrations of toxin. Note the swelling(s) of capillary endothelium and the numerous red blood cells in the capillary lumen. b: Illustrates early changes in animals exposed to low concentrations of toxin (ie, fibrin (f) in the capillary lumen and osmophilic inclusions (i) in the visceral epithelial cells). c: A capillary loop with significant fibrin (f) deposits. Uranyl acetate, lead citrate; bar, 5 μm.

Light micrographs of 1-μm plastic sections of renal proximal tubules from an animal exposed to high concentrations of toxin (a, c, and e) and a similar animal exposed to low concentrations of toxin (b, d, and f). a: Normal clear vacuoles in the epithelium and a normal-appearing brush border and peritubular capillary from an animal exposed to high toxin. b: Osmophilic inclusions in the epithelium and an intact brush border. c: Early epithelial degeneration manifested by loss of the brush border (arrows). d: Frank extrusion of epithelial cytoplasmic blebs, some with organelles (arrow) and some without. Note that the cells with the more extensive extrusions have lost more of their brush border. e: No damage to tubular epithelium. f: Widespread tubular epithelial cell damage. Paragon stain; bar, 20 μm.

Light micrographs of 1-μm plastic sections of small intestinal villi from animals exposed to high concentrations of toxin (a and c) and an animal exposed to low concentrations of toxin (b and d). a: The tip of the villus from a high-toxin-dose animal has deteriorated, the epithelial layer is lost, and a lacteal (L) is filled with blood. Bar, 50 μm. b: A villous tip from a low-toxin-dose animal is essentially normal except for an increase in inflammatory cells near the tip. The lacteal (L) is clear. Bar, 50 μm. c: The base of the villus from a high-toxin-dose animal shows congested capillaries (arrows) and a blood-filled lacteal (L). Bar, 20 μm. d: A villous tip from a low-toxin-dose animal shows macrophages scattered in the lamina propria near the tip. The capillaries (arrows) appear normal with no congestion. The lacteal (L) is near normal with only an occasional red cell in its space. Bar, 20 μm. Uranyl acetate, lead citrate.

Electron micrograph of brain tissue from an animal exposed to high levels of toxin. A: Cross section of a normal microvessel (ne, normal endothelial cell) surrounded by normal glial elements. Note the separation of the myelin (arrows), particularly in the large fibers. The preservation of the mitochondria throughout the tissue suggest that the myelin changes are not due to poor fixation. rc, red cell. Bar, 5 μm. B: Longitudinal section of a normal-appearing microvessel with some perivascular edema (e) and myelin separation (arrows). rc, red cell. Bar, 10 μm. Uranyl acetate, lead citrate.